Thesis

Distribution and conservation of reduced P metabolism operons in bacteria

P has long been considered a biologically inert yet essential element to all living organisms. However, our understanding of how P compounds are converted and made available for growth in the environment is greatly lacking. This deficit in our knowledge of P metabolism in an environmental context is highlighted by recent studies demonstrating that common soil bacteria are capable of oxidizing and reducing P compounds, thus altering P bioavailability in the environment. Understanding the interactions between these reduced P compounds and microbial populations is crucial to our understanding of P nutrient availability and management in the environment. These deficits in our knowledge led to our desire to identify novel reduce P oxidation pathways. Towards this end, DNA sequencing and analysis of the phosphite oxidation pathway in Pseudomonas putida AW2 were completed. The similarity of this pathway to previously characterized ptx operons suggested recent horizontal gene transfer. The industrial use of hypophosphite and phosphite is likely leading to increased concentrations of these compounds in the environment. Database mining was used to look for further evidence of horizontal gene transfer of these operons, which would suggest that bacteria are adapting to these environmental changes. Sixty-four organisms were identified that harbor genes allowing the oxidation of hypophosphite, phosphite or both compounds. Recent horizontal gene transfer was evident in both of these pathways. HtxA was 100 percent conserved in four of the five bacteria identified as having HtxA. Seven examples of recent cross genus horizontal gene transfer of PtxD were identified. ptxD was found in association with heavy metal detoxification genes in several organisms, suggesting that it may play a role in the detoxification of phosphite in the environment. Finally, the divergent evolution of two distinct lineages C-P lyase operon, designated phn and htx were demonstrated. These findings indicate that reduced P compounds have been, and are currently important sources of P in the environment, and that diverse bacterial species play an essential role in the bioavailability of P.

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